Bytecode, also known as p-code (portable code), is a form of instruction set designed for efficient execution by a software interpreter. Unlike human-readable source code, bytecodes are compact numeric codes, constants, and references (normally numeric addresses) which encode the result of parsing and semantic analysis of things like type, scope, and nesting depths of program objects. They therefore allow much better performance than direct interpretation of source code.

The name bytecode stems from instruction sets which have one-byte opcodes followed by optional parameters. Intermediate representations such as bytecode may be output by programming language implementations to ease interpretation, or it may be used to reduce hardware and operating system dependence by allowing the same code to run on different platforms. Bytecode may often be either directly executed on a virtual machine (i.e. interpreter), or it may be further compiled into machine code for better performance.

Since bytecode instructions are processed by software, they may be arbitrarily complex, but are nonetheless often akin to traditional hardware instructions; virtual stack machines are the most common, but virtual register machines have also been built. Different parts may often be stored in separate files, similar to object modules, but dynamically loaded during execution.

Jan Koster (born July 8, 1945 in Delft) is a Dutch linguist and professor emeritus at the University of Groningen in The Netherlands.

He studied at the University of Amsterdam, where, after visiting MIT (Cambridge, Massachusetts, 1976), he received his PhD in 1978. Before moving to Groningen (in 1986), Koster was assistant professor at the University of Amsterdam and Utrecht University, and associate professor at Tilburg University.

With Henk van Riemsdijk and Jean-Roger Vergnaud, Koster was one of the founders of GLOW, the major European organization of generative linguistics. He was co-founder and editor of The Linguistic Review and is currently co-editor (with van Riemsdijk and Harry van der Hulst) of Studies in Generative Grammar (published by Mouton de Gruyter). He specializes in theoretical syntax and the philosophy and history of linguistics. He made notable contributions to the theories of word order, locality and anaphora.

Home page Jan Koster (University of Groningen)